U.S. patent application number 09/843973 was filed with the patent office on 2002-10-31 for torque device for electronic steer-by wire steering systems.
This patent application is currently assigned to EATON CORPORATION .. Invention is credited to Hjelsand, Timothy A., Rasmussen, Kenneth G..
Application Number | 20020157894 09/843973 |
Document ID | / |
Family ID | 25291453 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157894 |
Kind Code |
A1 |
Hjelsand, Timothy A. ; et
al. |
October 31, 2002 |
Torque device for electronic steer-by wire steering systems
Abstract
A steer-by-wire vehicle steering system and method of
controlling such a steering system when steering into and away from
a steering stop. In one embodiment, the system includes a steering
reaction device (55) including a fluid displacement mechanism (71),
and a valve arrangement (95) operable to vary the steering reaction
provided to the vehicle operator. In another embodiment, there is a
"friction" reaction device (111) including an electromagnetic coil
(115) which can have a varying signal (61) applied to it to vary
the steering reaction the coil imposes on a movable member (113) of
the device (111). In either embodiment, the reaction device
includes a spring arrangement (93;131), such that rotation of the
steering wheel (51) is in opposition to a spring force. In
accordance with the method of the invention, as the operator steers
into a stop, the reaction torque increases enough to prevent
turning the steering wheel (51) further, but when the operator
turns the wheel to steer away from the stop, the system senses the
reversed direction of steering and reduces substantially the
steering reaction which the operator senses.
Inventors: |
Hjelsand, Timothy A.;
(Waconia, MN) ; Rasmussen, Kenneth G.; (Maple
Grove, MN) |
Correspondence
Address: |
EATON CORPORATION
EATON CENTER
1111 SUPERIOR AVENUE
CLEVELAND
OH
44114
|
Assignee: |
EATON CORPORATION .
Eaton Center 1111 Superior Avenue
Cleveland
OH
|
Family ID: |
25291453 |
Appl. No.: |
09/843973 |
Filed: |
April 26, 2001 |
Current U.S.
Class: |
180/446 ;
180/403 |
Current CPC
Class: |
B62D 5/097 20130101;
B62D 5/003 20130101; B62D 5/0832 20130101; B62D 6/008 20130101 |
Class at
Publication: |
180/446 ;
180/403 |
International
Class: |
B62D 005/04 |
Claims
1. A steer-by-wire vehicle steering system including a steered
wheel actuator assembly operable to provide steering movement to a
pair of steered wheels in response to changes in an input signal; a
controller operable to generate said input signal for transmittal
to said steered wheel actuator assembly, and to generate a feedback
signal; a steering actuator assembly including a steering input
device adapted to receive a steering input motion from a vehicle
operator, a steering reaction device adapted to be driven by said
steering input device and to provide a steering reaction to the
vehicle operator, and a steering motion sensor adapted to sense
said steering input motion and transmit a motion signal to said
controller; and said steering actuator assembly including means
operable to vary said steering reaction provided to the vehicle
operator in response to variations in said feedback signal
generated by said controller; characterized by: (a) said steering
reaction device comprises a housing defining a fluid inlet port and
a fluid outlet port, a fluid displacement mechanism, and valving
operable to control the flow of fluid from said inlet port through
said displacement mechanism to said outlet port in response to
movement of said steering input device; (b) said valving defining a
neutral condition blocking fluid flow through said displacement
mechanism, and including means biasing said valving toward said
neutral condition.
2. A steer-by-wire vehicle steering system as claimed in claim 1,
characterized by said steering motion sensor being disposed between
said steering input device and said biasing means, whereby said
steering input device and said steering motion sensor may be
rotated even when said feedback signal is such that said means
operable to vary said steering reaction effectively prevents
rotation of said fluid displacement mechanism.
3. A steer-by-wire vehicle steering system as claimed in claim 1,
characterized by said steered wheel actuator assembly comprises a
fluid pressure operated steering device and a proportional steering
valve, operable to control fluid flow from a source of pressurized
fluid to said fluid pressure operated steering device in response
to changes in said input signal.
4. A steer-by-wire vehicle steering system as claimed in claim 1,
characterized by said means operable to vary said steering reaction
comprises a valve arrangement disposed in series fluid
communication between said fluid inlet port and said fluid outlet
port, said valve arrangement being operable to vary the restriction
to fluid flow through said steering reaction device, and through
said fluid displacement mechanism, in response to variations in
said feedback signal.
5. A steer-by-wire vehicle steering system as claimed in claim 1,
characterized by said valving comprises a primary, rotatable valve
member, rotatable in response to rotation of said steering input
device, and a relatively rotatable, follow-up valve member,
rotatable in response to rotation of said fluid displacement
mechanism, said biasing means comprising a biasing spring
arrangement operably disposed between said primary valve member and
said follow-up valve member, and operable to bias said valve
members toward a neutral rotational position relative to each
other.
6. In a steering system of the type including a friction type
steering reaction device adapted to receive a manual steering
input, the reaction device including a first member and friction
reaction means operable to resist rotation of said first member;
characterized by: (a) said friction reaction device including a
first shaft fixed to rotate with said manual steering input, and a
second shaft fixed to rotate with said first member of said
friction reaction device; (b) a spring biasing arrangement having a
first end seated relative to said first shaft and a second end
seated relative to said second shaft; (c) said first shaft and said
second shaft being configured to permit a predetermined rotational
displacement therebetween in opposition to an increasing biasing
force exerted by said spring biasing arrangement.
7. A steering system as claimed in claim 6, characterized by a
steering motion sensor being disposed between said manual steering
input and said spring biasing arrangement, whereby said manual
steering input and said steering motion sensor may rotate even when
said feedback signal is such that said friction reaction means
operable to resist rotation of said first member effectively
prevents rotation of said first member and said second shaft.
8. A steering system as claimed in claim 6, characterized by said
friction reaction means comprises a housing member defining a
chamber, said first member being rotatably disposed within said
chamber, said housing member having operably associated therewith
an electromagnetic coil operable in response to variations in a
feedback signal to vary a reaction torque imposed on said first
member.
9. A steering system as claimed in claim 6, characterized by said
steered wheel actuator assembly comprises a fluid pressure operated
steering device and a proportional steering valve, operable to
control fluid flow from a source of pressurized fluid to said fluid
pressure operated steering device in response to changes in an
input signal generated by a controller.
10. A method of controlling a steering system when steering into
and away from a steering stop, the steering system being of the
type including a steered wheel actuator assembly operable to
provide steering movement to a pair of steered wheels; a controller
operable to generate a feedback signal to a steering actuator
assembly including a steering input device, and a steering reaction
device adapted to be driven by said steering input device, and a
steering motion sensor adapted to sense said steering input motion
and transmit a steering motion signal to said controller; the
steering reaction device including means operable to vary said
steering reaction in response to variations in said feedback
signal; said method comprising the steps of: (a) moving said
steering input device to cause said steered wheel actuator assembly
to approach said steering stop, while storing energy in a biasing
spring and generating a steered wheel position signal indicative of
at-the-stop steering; (b) providing system logic within said
controller to read said at-the-stop signal and generate a feedback
signal also indicative of at-the-stop steering; (c) transmitting
said feedback signal to said means operable to vary said steering
reaction, whereby said steering reaction increases to a maximum as
said steered wheel actuator assembly reaches said steering stop;
(d) allowing said steering input device to move in a reverse
direction, corresponding to said steered wheel actuator assembly
moving away from said steering stop, under the influence of said
biasing spring, thereby generating a motion signal indicative of
said reverse direction; and (e) transmitting said motion signal to
said controller to generate a new feedback signal indicative of
said reverse direction of steering, and transmitting said new
feedback signal to said means operable to vary said steering
reaction, whereby said steering reaction is decreased substantially
from said maximum reaction.
11. A method as claimed in claim 10, characterized by, in step (c),
said steering reaction increases such that said steering input
device cannot thereafter be moved, in the same direction, by normal
operator steering input.
Description
BACKGROUND OF THE DISCLOSURE
[0001] The present invention relates to power steering systems, and
more particularly to such steering systems of the type which are
typically referred to as being of the "steer-by wire" type.
[0002] As will be understood by those skilled in the art, a typical
steer-by-wire system is to be distinguished from the known, prior
art vehicle steering systems of the following types:
[0003] (1) mechanical steering systems, in which there is a
mechanical link between the steering wheel and the steered wheels
and the entire steering torque to the steered wheels is merely the
result of steering input effort provided by the vehicle
operator;
[0004] (2) mechanical steering with hydraulic power assist, in
which there is a mechanical link between the steering wheel and the
steered wheels, but the operator input is assisted by hydrostatic
fluid pressure acting on, for example, opposite ends of a rack and
pinion device; and
[0005] (3) a fully hydrostatic power steering system, in which
there is no mechanical link between the steering wheel and the
steered wheels, and all steering torque is the result of
hydrostatic fluid pressure communicated to a steering actuator from
a steering control unit (SCU), the input to which is the manual
steering effort of the operator.
[0006] A typical steer-by-wire system could be a type of
hydrostatic power steering system, but could also be a fully
electric steering system, as will be explained in greater detail
subsequently. In the typical steer-by-wire system, the rotation of
the steering wheel by the vehicle operator is sensed, and results
in the generation of a steering command signal which is transmitted
as one of the inputs to an electrical logic device, such as the
vehicle microprocessor. Another input to the microprocessor is the
instantaneous steered wheel position, typically generated by a
sensor associated with the steering cylinder. In response to the
various input signals received, the microprocessor transmits a
control signal to a proportional steering valve, which controls the
flow of fluid from a steering pump to the steering cylinder.
Therefore, the only "connection" between the vehicle operator and
the steering valve is the electrical command signal (wire) from the
microprocessor, and hence, the name "steer-by-wire".
[0007] Steer-by-wire systems are becoming increasingly popular on a
variety of vehicle applications. In the conventional fully
hydrostatic power steering system, there is a steering input device
(such as the SCU), which receives its input from the steering wheel
by means of the steering column, and therefore, the SCU is
typically disposed in, or immediately adjacent the operator
compartment. In such a hydrostatic steering system, all of the flow
within the steering system passes through the SCU, and therefore,
there is a large flow of pressurized fluid in close proximity to
the operator compartment. As a result, there is likely to be the
noise and vibration normally associated with the flow of
pressurized fluid, readily discernible by the operator. In the case
of a steer-by-wire system, the steering input device disposed in or
near the operator compartment does not have the steering system
fluid flow passing through it. Only the proportional steering valve
has substantial fluid flow passing through it, but the proportional
steering valve is typically mounted somewhere near the steering
cylinder, well away from the operator compartment. Therefore, the
device which constitutes the major source of noise and vibration in
a hydrostatic power steering system is eliminated in a
steer-by-wire system, and replaced by a valve which does not have
to be located in or near the operator compartment.
[0008] One of the problems associated with the typical, prior art
steer-by-wire steering system is a relatively poor "torque feel".
In many such systems, the input portion of the system merely
comprises a steering wheel and steering column, and the associated
sensors needed to sense steering wheel position, rate of rotation,
etc. As a result, when the vehicle operator turns the steering
wheel to accomplish a steering maneuver, there is very little
torque feel of the type the operator would normally experience when
rotating the steering wheel in any of the known
mechanical/hydrostatic systems described above.
[0009] In many vehicle applications, it would be desirable for the
steer-by-wire system to have not only an appropriate level of
torque feel, but also, the ability for the system to vary the
torque feel to correspond to changes in the various steering system
parameters. For example, as one system design option, the
steer-by-wire system could be made to have a feel which is very
similar to what the operator would normally experience in driving
an automobile, in which the reaction torque could be made to
decrease as the vehicle speed increases. Alternatively, the
steer-by-wire system could be made to have a feel similar to
conventional hydrostatic power steering in which the torque feel
could be made to increase as the vehicle operator would increase
the rate of rotation of the steering wheel.
[0010] Finally, it would be desirable for the torque feel to
greatly increase, to the point of effectively preventing further
rotation of the steering wheel, whenever the steered wheels
approach the "stops", i.e., when the steered wheels reach their
maximum steering angle. Unfortunately, in some prior art systems,
the attempt to increase the reaction torque as the operator steers
into a stop has merely hampered the subsequent steering operation
in the opposite direction, away from the stop. By way of example
only, in some systems which have been proposed, the means which
provides the increased torque feel just before reaching the
steering stops would still be engaged or "applied" as the operator
would attempt to steer away from the stop, i.e., the torque feel
would be as great steering away from the stops as it was
approaching the stops, which is clearly undesirable.
BRIEF SUMMARY OF THE INVENTION
[0011] Accordingly, it is an object of the present invention to
provide an improved steer-by-wire vehicle power steering system
which overcomes the disadvantages of the prior art systems, and
which is capable of providing the vehicle operator with improved
torque feel.
[0012] It is a more specific object of the present invention to
provide such an improved steer-by-wire system which is also capable
of varying the torque feel experienced by the operator in response
to variations in vehicle and steering system operating
parameters.
[0013] It is a further object of the present invention to provide
such an improved steer-by-wire system which accomplishes the
above-stated objects, and which includes the ability to provide the
operator with substantially increased torque feel when the system
reaches the end of steering stops, while maintaining the ability to
steer easily away from the stop.
[0014] The above and other objects of the invention are
accomplished by the provision of an improved steer-by-wire vehicle
steering system including a steered wheel actuator assembly
operable to provide steering movement to a pair of steered wheels
in response to changes in an input signal. A controller is operable
to generate the input signal for transmittal to the steered wheel
actuator assembly, and to generate a feedback signal. A steering
actuator assembly includes a steering input device adapted to
receive a steering input motion from a vehicle operator, a steering
reaction device adapted to be driven by the steering input device
and to provide a steering reaction to the vehicle operator, and a
steering motion sensor adapted to sense the steering input motion
and transmit a motion signal to the controller. The steering
actuator assembly includes means operable to vary the steering
reaction provided to the vehicle operator in response to variations
in the feedback signal generated by the controller.
[0015] The improved steer-by-wire vehicle steering system is
characterized by the steering reaction device comprising a housing
defining a fluid inlet port and a fluid outlet port, a fluid
displacement mechanism, and valving operable to control the flow of
fluid from the inlet port through the displacement mechanism to the
outlet port in response to movement of the steering input device.
The valving defines a neutral condition blocking fluid flow through
the displacement mechanism, and includes means biasing the valving
toward the neutral condition.
[0016] In accordance with another aspect of the invention, an
improved steering system is provided of the type including a
friction type steering reaction device adapted to receive a manual
steering input, the reaction device including a first member and
friction reaction means to resist rotation of the first member.
[0017] The improved steering system is characterized by the
reaction device including a spool member fixed to rotate with the
manual steering input, and a sleeve member fixed to rotate with the
first member of the reaction device, and at least partially
surrounding the spool member. A spring biasing arrangement has a
first end seated relative to the spool member and a second end
seated relative to the sleeve member. The spool member and the
sleeve member are configured to permit a predetermined rotational
displacement between the spool member and the sleeve member in
opposition to an increasing biasing force exerted by the spring
biasing arrangement.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is an overall system schematic of one embodiment of a
steer-by-wire vehicle steering system of the type to which the
present invention relates.
[0019] FIG. 2 is a hydraulic schematic of one embodiment of the
steering actuator assembly which is shown as part of the system
schematic of FIG. 1.
[0020] FIG. 3 is an axial cross-section of the steering actuator
assembly shown schematically in FIG. 2.
[0021] FIG. 3A is a transverse cross-section taken on line A-A of
FIG. 3, illustrating the centering spring arrangement utilized as
one aspect of the present invention.
[0022] FIG. 4 is a graph of steering reaction ("Torque") vs. speed
of steering wheel rotation ("R.P.M."), illustrating one important
aspect of the present invention.
[0023] FIG. 5 is a somewhat schematic, exploded, perspective view
of an alternative embodiment of the steering actuator assembly of
the present invention.
[0024] FIG. 5A is a fragmentary, flat plan view of a portion of the
alternative embodiment of FIG. 5, illustrating one important aspect
of the alternative embodiment.
[0025] FIG. 6 is a logic diagram illustrating the control logic,
which comprises one important aspect of the invention, and which
may be utilized in connection with the steering actuator assembly
of the present invention, regardless of which embodiment of
actuator is utilized.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] Referring now to the drawings, which are not intended to
limit the invention, FIG. 1 is an overall schematic one embodiment
of a steer-by-wire vehicle steering system of the type with which
the present invention may be utilized. The steer-by-wire steering
system shown schematically in FIG. 1 includes a steered wheel
actuator assembly, generally designated 11; a vehicle fluid
pressure source, generally designated 13; a vehicle microprocessor
(or electronic control unit, ECU), generally designated 15; and a
steering actuator assembly, generally designated 17. As was noted
previously, instead of a system which is basically a hydrostatic
power system such as that shown in FIG. 1, the present invention
could be utilized with a steering system which is all electrical,
in which case, by way of example only, the steered wheel actuator
assembly 11 could comprise an electric motor of either the rotary
or linear type.
[0027] The steered wheel actuator assembly 11 of the preferred
embodiment includes a steering cylinder 19 shown schematically in
FIG. 1 as having a piston rod 21 extending from each end of the
cylinder 19. The piston rods 21 would be operably associated with
the steered wheels (not shown) of the vehicle in any conventional
manner, the details of which are not essential features of the
present invention. Shown schematically in FIG. 1 is a steered wheel
position sensor 23, which senses the linear position of the
adjacent piston rod 21 and transmits an electrical signal 25 to the
ECU 15, the signal 25 being representative of the instantaneous
steered wheel position, as is now quite well known to those skilled
in the steering art.
[0028] The steered wheel actuator assembly 11 also includes a
proportional steering valve 27 which may comprise any of a number
of well known proportional valves. Typically, the steering valve 27
would comprise a conventional three-position, four-way,
electromagnetically operated valve assembly having its outlet ports
connected by means of a pair of conduits 29 and 31 to the opposite
ends of the steering cylinder 19. The operation of the steering
valve 27, from a normal, neutral condition to either a left turn or
right turn condition, occurs in response to changes in an input
command signal 33, transmitted from the ECU 15 to the steering
valve 27.
[0029] The vehicle fluid pressure source 13 comprises a fluid pump
35, shown schematically herein as being a fixed displacement pump,
which receives fluid from a reservoir 37. The pump 35 is driven by
an electric motor 39, in response to an electrical signal 41
transmitted to the motor 39 from the ECU 15. The fluid output of
the pump 35 is communicated by means of a conduit 43 to a load
sensing priority flow control valve (LSPV), generally designated
45, which may be of the general type illustrated and described in
U.S. Pat. No. 3,455,210, assigned to the assignee of the present
invention and incorporated herein by reference. The LSPV 45
responds to a load signal 47 to apportion fluid between the
priority device, i.e., the steering valve 27, and an auxiliary
circuit 49, which may comprise any one of a number of hydraulic
functions on the particular vehicle (typically, a function other
than steering or brakes). The load signal 47, communicated to the
LSPV 45 from the steering valve 27, is representative of the load
imposed on the actuator assembly 11 during steering.
[0030] The steering actuator assembly 17 includes a conventional
steering wheel 51 and steering column 53 which receive the steering
input motion from the operator and transmit that motion to a
steering input device 55. The steering input device 55 includes, or
has disposed adjacent thereto, some sort of steering input sensor
57 which transmits to the ECU 15 an electrical signal 59
corresponding to the motion of the steering wheel 51. Preferably,
the steering input signal 59 will provide to the ECU 15, and to the
system logic contained therein, at least the following
information:
[0031] (1) whether or not the steering wheel 51 is moving;
[0032] (2) if so, in which direction (CW or CCW) is the steering
wheel 51 moving; and
[0033] (3) what is the instantaneous speed of rotation of the
steering wheel 51.
[0034] As will be explained in greater detail subsequently, the ECU
15 transmits to the input device 55 an electrical signal 61 which
is representative of the instantaneous level of reaction torque
which is appropriate for the system, under the conditions which
exist at that point in time. It should be understood that
hereinafter, and in the appended claims, the terms "reaction
torque"; "steering reaction"; "torque feel" and perhaps other terms
of similar import are used synonymously, and are understood to be
equivalent. Therefore, it should be understood by those skilled in
the art that the steering input device 55 could take many forms,
several of which will be illustrated and described herein in
greater detail subsequently. It also should be understood by those
skilled in the art, from a reading and understanding of this
specification, that the details of the input device 55 are not
essential features of the invention, except to the extent set forth
in the appended claims. What is important in regard to the steering
input device 55 is that it provide the vehicle operator with an
appropriate level of reaction torque, in response to rotation of
the steering wheel 51. Preferably, a portion of the reaction torque
is inherent in the steering input device 55, and the remainder of
the reaction torque occurs in response to the electrical signal 61,
as will be explained in greater detail subsequently.
[0035] Referring now primarily to FIGS. 2 and 3, one embodiment of
the steering input device 55 will be described. The device 55 may
be made generally in accordance with the teachings of U.S. Pat.
Nos. 4,936,094 and 5,873,243, both of which are assigned to the
assignee of the present invention and incorporated herein by
reference. The device 55 does, however, vary from the devices
illustrated in the above-incorporated patents, as will become
apparent subsequently to those skilled in the art, upon a reading
and understanding of the present specification.
[0036] Referring now primarily to FIG. 3, but also to FIG. 2 as
appropriate, the steering input device 55 comprises a plurality of
sections held in tight sealing engagement by a plurality of bolts
63, including a valve housing section 65, and attached thereto, a
front end cap 67. In the subject embodiment, and by way of example
only, the steering input sensor 57 comprises a separate forward
housing section attached to the front end cap 67, and disposed
therein is a rotary sensor disc 58. Disposed at the rearward end of
the housing section 65 is a wear plate 69, a gerotor displacement
mechanism, generally designated 71, and a rearward end cap 73. In a
manner well know to those skilled in the art, the gerotor
displacement mechanism 71 includes an internally toothed ring
member 75 and an externally toothed star member 77 which is
eccentrically disposed within the ring member 75 for orbital and
rotational movement therein. Other types of fluid displacement
mechanisms may be used, instead of gerotor gear sets, examples of
such other mechanisms being devices of the gear type, or of the
sliding vane type.
[0037] The valve housing section 65 defines a valve bore 79, and
disposed therein is a valving arrangement, generally designated 81
(see FIG. 2). In the subject embodiment, and by way of example
only, the valving arrangement 81 includes a primary rotatable valve
member 83 (spool valve), and a relatively rotatable, follow-up
valve member 85 (sleeve valve). The spool valve 83 typically has,
at its forward end (left end in FIG. 3) a set of internal splines
87 for engagement with mating external splines (not shown herein)
on the steering column 53, such that rotation of the steering wheel
51 and the steering column 53 results in rotation of the spool
valve 83.
[0038] As is well know to those skilled in the art of hydrostatic
steering valves, one function of the gerotor displacement mechanism
71 is to measure the volume of fluid flow through the mechanism 71
(also referred to as a "fluid meter"), and transmit a follow-up
movement to the valving arrangement 81 which is proportional to the
flow through the fluid meter 71. More particularly, the follow-up
movement is transmitted to the sleeve valve 85 by means of a main
drive shaft 89, which is preferably in splined engagement with the
star 77. The rotational follow up motion of the forward end of the
shaft 89 is transmitted to the sleeve valve 85 by means of a
transverse pin 91 which passes through circumferentially elongated
openings in the spool valve 83 and has its ends received within
close-fit bores in the sleeve valve 85, as is quite well known in
the SCU art.
[0039] In accordance with one important aspect of the invention,
there is a biasing spring arrangement 93, the function of which is
to bias the spool valve 83 toward its centered, neutral position (N
in FIG. 2) relative to the sleeve valve 85, as is also quite well
known in the SCU art. Therefore, any rotation of the steering wheel
51 by the vehicle operator is in opposition to the biasing force of
the spring arrangement 93, providing a certain minimum reaction
torque or steering reaction corresponding to the line marked "MIN."
in the graph of FIG. 4. Further reference will be made to the graph
of FIG. 4 in connection with the remaining description of the
embodiment of FIGS. 2 and 3.
[0040] Referring still primarily to FIGS. 2 and 3, attached to the
valve housing section 65, by any suitable means, is a port block
valve, generally designated 95, including a moveable valve member
97 (see FIG. 2), which is preferably operated by means of an
electromagnetic coil 99. The valve housing section 65 defines a
fluid inlet port 101 and a fluid outlet port 103, both of which are
shown only schematically, and only in FIG. 2. As is well known to
those skilled in the SCU art, a typical SCU for use in a
hydrostatic power steering system would have, in addition to an
inlet port and an outlet port, a pair of control ports connected to
the steering cylinder. However, the steering input device 55 of the
invention looks, in axial cross-section, like a conventional SCU,
but it has only 2 ports, the inlet port 101 and the outlet port
103, in the same manner as a "torque generating" steering device.
Such a torque generating device is illustrated and described in
greater detail in above-incorporated U.S. Pat. No. 4,936,094.
Therefore, the spool valve 83 and the sleeve valve 85 of the
subject embodiment will be clearly understood from the cited '094
patent.
[0041] Preferably, the valve member 97 is a two position, three-way
valve, having two of its ports connected to the ports 101 and 103,
and its third port 105 connected to the system reservoir 37. The
general function of the port block valve 95 is to provide a
restriction to the flow of fluid within the steering input device
55, thus providing reaction torque over and above that provided by
the spring arrangement 93 (refer again to the graph of FIG. 4). In
accordance with one aspect of the present invention, the amount of
additional reaction torque experienced by the operator while
rotating the steering wheel 51 is determined by the position of the
valve member 97, and in turn, the position of the valve member 97
is determined by the level of the electrical signal 61 received
from the ECU 15, as will be described in greater detail
subsequently. With the valve member 97 in the position shown in
FIG. 2, there is relatively little restriction to flow because the
ports 101 and 103 are interconnected by the valve member 97 such
that, as the operator rotates the steering wheel 51, there is only
minimal resistance to fluid flow through the valving arrangement 81
(turned to either the right turn ("R") or left turn ("L") position
in FIG. 2), through the fluid meter 71, and through the port block
valve 95.
[0042] As the valve member 97 is moved from the "connected"
position shown in FIG. 2 toward the opposite, "blocked" position,
the resistance to fluid flow through the steering input device 55
increases, increasing the reaction torque on the steering wheel 51.
For example, the ECU 15 constantly reads and compares the
electrical signal 59 (steering wheel position) and the electrical
signal 25 (steered wheel position) and generates a signal
representative of the difference ("error") between the signals 59
and 25. The signal 61 which actuates the valve member 97 from its
connected position toward its blocked position would be generally
proportional to the error between the steering and steered wheel
positions, or stated another way, the greater the instantaneous
error, the greater would be the reaction torque added to the system
by means of the port block valve 95. As another example of the
variability of the reaction torque, the ECU 15 may be programmed
such that the electrical signal 61 is inversely proportional to
vehicle speed, i.e., as the vehicle speed increases (with all other
variables remaining constant), the signal 61 decreases, thus moving
the valve member 95 toward the "connected" position shown in FIG.
2, reducing the reaction torque on the system. This latter example
would be consistent with the feel of a conventional automotive
power steering system.
[0043] Referring now primarily to FIG. 5, there is illustrated
another embodiment of the steering input device, in which like
elements bear like reference numerals, and new, or substantially
modified elements bear reference numerals in excess of "110".
Although the embodiment of FIG. 5 is quite different structurally
than that of FIGS. 2 and 3, it is important to note that, at least
theoretically, the vehicle operator should not be aware of the
difference between the two embodiments, i.e., the steering reaction
should feel the same to the operator with either embodiment.
[0044] In FIG. 5, which is meant to be somewhat schematic, there is
shown a "friction reaction device", generally designated 111,
including an annular housing 112, which defines an internal annular
chamber within which is disposed a brake disc 113. The term
"friction" is used herein in a generic sense to include true
friction (mechanical contact) devices, as well as those, such as
the device 111 which are electromagnetic, but typically don't
involve actual contact between the relatively rotatable members.
Disposed within the annular housing 112 is an electromagnetic coil
115, connected electrically to the ECU 15 by means of a pair of
electrical leads which transmit to the coil 115 the electrical
signal 61, shown schematically in FIGS. 1 and 2. Preferably, a
predetermined, minimum current would be maintained across the coil
115, thus providing a predetermined, minimum reaction torque
required to rotate the brake disc 113.
[0045] Attached to the brake disc 113, and extending axially
forward therefrom (to the left in FIG. 5), is a shaft member 117
which defines an axially-extending slot 119 in which is disposed a
key member 121. The slot 119 opens, toward its left end in FIG. 5,
into a larger slot portion 123. The left end of the shaft 117 is
received within a cylindrical sleeve-like member 125, which also
defines an axially-extending slot 127, opening toward its right end
into a larger slot portion 129, which serves as the rotational
stops for the key member 121 and sleeve-like member 125, as may
best be seen in FIG. 5A. Although the alternative embodiment has
been described, by way of example only, with the shaft member 117
extending from the brake disc 113, and the sleeve-like member 125
extending from the steering column 53, those skilled in the art
will understand that, within the scope of the invention, this
arrangement is not essential, and could be reversed. All that is
essential is that there be some such arrangement of shafts (spools)
and sleeves and a spring and some means to limit relative rotation
within the assembly.
[0046] Surrounding the sleeve-like member 125 is a generally
annular torsion spring 131 having a pair of inwardly-extending ends
or tabs 133 which are received within the slot 127 of the
sleeve-like member 125, and extend radially into the larger slot
portion 123 of the shaft member 117. The spring 131, just
described, functions in basically the same manner as the centering
spring arrangement 93 of the main embodiment, and the key member
121 within the larger slot portion 129 functions in basically the
same manner as the transverse pin 91 in the main embodiment. In
either case, the spring permits rotation of the steering wheel 51,
but with a certain steering reaction occurring, and the pin 91 (or
key member 121) limits the amount of relative rotation which can
occur between the steering wheel 51 and the friction reaction
device (the fluid displacement mechanism 71 or the electromagnetic
device 111).
[0047] In operation, the beginning of rotation of the steering
wheel 51 results in compression of the springs (93 or 131) because
in either embodiment, there is a certain, minimum break away torque
in the friction device (55 or 111). In the case of the hydraulic
steering input device 55 of the main embodiment, the minimum break
away torque is achieved by blocking the normal commutation ports in
the valving 81, thus preventing rotation of the fluid displacement
mechanism 71 until there is sufficient relative rotation of the
spool valve 83 and sleeve valve 85 to open the commutation ports,
which are well known to those skilled in the art, and are
illustrated and described in the above-incorporated patents. In the
case of the friction reaction device 111, the break away torque is
set by a predetermined, minimum voltage applied to the coil 115.
Note the minimum value of V (voltage) associated with the
determination of the constants K1 and K2 in FIG. 6. Alternatively,
and as is well known in the electromagnetic art, a certain residual
magnetic field strength could be built into the device 111 to
achieve the minimum reaction torque.
[0048] As rotation of the steering wheel 51 continues, the springs
are compressed sufficiently to overcome the minimum break away
torque of the friction device (55 or 111) so that the friction
device itself begins to rotate (i.e., the star 77 or the brake disc
113). Rotation of the steering column 53 is sensed by the steering
motion sensor (57), resulting in the generation of an appropriate
command signal 33 which is transmitted to the proportional steering
valve 27, controlling the movement of the valve 27 to control the
flow of fluid to the steering cylinder 19. Steering cylinder
position is sensed by the sensor 23 and the position signal 25 is
transmitted to the ECU 15, wherein the signal 25 is compared to the
steering wheel position signal 59, as shown in FIG. 6, to generate
an error signal which, when multiplied by the constant K1, results
in an appropriate signal 61.
[0049] The signal 61 is then sent to the friction device (and
specifically, to either the coil 99 or the coil 115) to vary the
steering reaction torque in accordance with the predetermined
relationship. In either embodiment, an increase in the voltage to
the coil (99 or 115) would cause an increase in the torque required
to rotate the friction device which, in turn, would cause an
increased compression of the springs (93 or 131) and therefore, an
increased torque reaction at the steering wheel 51.
[0050] It should be noted that, in either embodiment of the
steering input device, the "order" of the of the elements in the
torque path (which may not be the same as the physical arrangement
of the elements) is the same, starting with the steering wheel 51,
then the steering column 53, then the steering input sensor 57,
then the centering (biasing) spring arrangement 93 (or 131), then,
finally, the reaction device, i.e., the device which produces the
steering reaction. As a result, in either embodiment, the
steering-at-the-stops functions in the same manner. When the
steering cylinder 19 approaches the end of its travel (the
"stops"), electrical signal 25 which is transmitted to the ECU 15
is operated upon by the system logic to produce a signal 61 ("FULL
ON" in FIG. 6) which, in the case of the main embodiment, will move
the valve member 97 fully to the blocked position shown in FIG. 2,
blocking flow through the ports 101 and 103. Thus, the fluid
displacement mechanism 71 will not rotate any further, and when the
spring arrangement 93 is fully compressed, the operator would sense
an abrupt increase in the reaction torque, and when the pin 91
reaches the end of its travel, the operator is unable to rotate the
steering wheel 51 any further.
[0051] Similarly, when the signal 61 ("FULL ON") corresponding to
end-of-stop steering is transmitted to the friction brake assembly
of FIG. 5, the coil 115 will apply sufficient torque to the brake
disc 113 to prevent any further rotation of the shaft member 117,
and when the spring 131 is fully compressed, and again the operator
senses an abrupt increase in the torque feel, and when the key
member 121 reaches the end of the slot portion 129, the operator is
unable to rotate the steering wheel 51 any further.
[0052] If the steering wheel 51 is then released by the operator,
the springs (93 or 131) would decompress, causing reverse rotation
of the steering wheel, but with the friction device still fully
engaged, and unable to rotate. However, the reverse movement of the
steering wheel 51 and steering column 53, under the influence of
the springs (93 or 131), is detected by the steering motion sensor
57, and an appropriate signal 59 transmitted to the ECU 15. In
order to have this capability (to steer easily away from the
stops), it is important that the spring deflection, when fully
compressed, is larger than the minimum resolution of the sensor 57.
For example, the springs 93 typically permit a relative rotation of
about 10 degrees between the spool valve 83 and the sleeve valve
85, while a typical sensor resolution would be about 1 or 2
degrees.
[0053] As was noted previously, one item of information carried by
the signal 59 is direction of rotation, so that the signal 59,
generated after the spring-influenced reverse rotation of the wheel
51, would inform the ECU 15 that steering away from the stops is
now occurring, and as a result, the signal 61 would be modified
(now "0") to "release" the friction device. With the friction
device now released, the operator is able to accomplish a normal
steering maneuver in the opposite direction.
[0054] The invention has been described in great detail in the
foregoing specification, and it is believed that various
alterations and modifications of the invention will become apparent
to those skilled in the art from a reading and understanding of the
specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come
within the scope of the appended claims.
* * * * *